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SubjectRe: [PATCH] dmaengine: qcom: bam_dma: Add LOCK and UNLOCK flag bit support
On 2021-02-09 23:05, Bjorn Andersson wrote:
> On Mon 01 Feb 09:50 CST 2021, mdalam@codeaurora.org wrote:
>
>> On 2021-02-01 12:13, Vinod Koul wrote:
>> > On 01-02-21, 11:52, mdalam@codeaurora.org wrote:
>> > > On 2021-02-01 11:35, Vinod Koul wrote:
>> > > > On 27-01-21, 23:56, mdalam@codeaurora.org wrote:
>> >
>> > > > > The actual LOCK/UNLOCK flag should be set on hardware command
>> > > > > descriptor.
>> > > > > so this flag setting should be done in DMA engine driver. The user
>> > > > > of the
>> > > > > DMA
>> > > > > driver like (in case of IPQ5018) Crypto can use flag
>> > > > > "DMA_PREP_LOCK" &
>> > > > > "DMA_PREP_UNLOCK"
>> > > > > while preparing CMD descriptor before submitting to the DMA
>> > > > > engine. In DMA
>> > > > > engine driver
>> > > > > we are checking these flasgs on CMD descriptor and setting actual
>> > > > > LOCK/UNLOCK flag on hardware
>> > > > > descriptor.
>> > > >
>> > > >
>> > > > I am not sure I comprehend this yet.. when is that we would need to do
>> > > > this... is this for each txn submitted to dmaengine.. or something
>> > > > else..
>> > >
>> > > Its not for each transaction submitted to dmaengine. We have to set
>> > > this
>> > > only
>> > > once on CMD descriptor. So when A53 crypto driver need to change
>> > > the crypto
>> > > configuration
>> > > then first it will lock the all other pipes using setting the LOCK
>> > > flag bit
>> > > on CMD
>> > > descriptor and then it can start the transaction , on data
>> > > descriptor this
>> > > flag will
>> > > not get set once all transaction will be completed the A53 crypto
>> > > driver
>> > > release the lock on
>> > > all other pipes using UNLOCK flag on CMD descriptor. So LOCK/UNLOCK
>> > > will be
>> > > only once and not for
>> > > the each transaction.
>> >
>> > Okay so why cant the bam driver check cmd descriptor and do lock/unlock
>> > as below, why do we need users to do this.
>> >
>> > if (flags & DMA_PREP_CMD) {
>> > do_lock_bam();
>>
>> User will not decide to do this LOCK/UNLOCK mechanism. It depends on
>> use case. This LOCK/UNLOCK mechanism not required always. It needs
>> only when hardware will be shared between different core with
>> different driver.
>
> So you have a single piece of crypto hardware and you're using the
> BAM's
> LOCK/UNLOCK feature to implement a "mutex" on a particular BAM channel?

Yes, In IPQ5018 SoC we are having only one Crypto and it will be
shared between
UBI32 core & A53 core, and these two cores are running different
driver to use Crypto.
The LOCK/UNLOCK flag can be set only on CMD descriptor.
>
>> The LOCK/UNLOCK flags provides SW to enter ordering between pipes
>> execution.
>> (Generally, the BAM pipes are total independent from each other and
>> work in
>> parallel manner).
>> This LOCK/UNLOCK flags are part of actual pipe hardware descriptor.
>>
>> Pipe descriptor having the following flags:
>> INT : Interrupt
>> EOT: End of transfer
>> EOB: End of block
>> NWD: Notify when done
>> CMD: Command
>> LOCK: Lock
>> UNLOCK: Unlock
>> etc.
>>
>> Here the BAM driver is common driver for (QPIC, Crypto, QUP etc. in
>> IPQ5018)
>> So here only Crypto will be shared b/w multiple cores so For crypto
>> request
>> only the LOCK/UNLOCK
>> mechanism required.
>> For other request like for QPIC driver, QUPT driver etc. its not
>> required.
>> So Crypto driver has to raise the flag for
>> LOCK/UNLOCK while preparing CMD descriptor. The actual locking will
>> happen
>> in BAM driver only using condition
>> if (flags & DMA_PREP_CMD) {
>> if (flags & DMA_PREP_LOCK)
>> desc->flags |= cpu_to_le16(DESC_FLAG_LOCK);
>> }
>>
>> So Crypto driver should set this flag DMA_PREP_LOCK while preparing
>> CMD
>> descriptor.
>> So LOCK should be set on actual hardware pipe descriptor with
>> descriptor
>> type CMD.
>>
>
> It sounds fairly clear that the actual descriptor modification must
> happen in the BAM driver, but the question in my mind is how this is
> exposed to the DMAengine clients (e.g. crypto, QPIC etc).

I have added these two flags "DMA_PREP_LOCK" & "DMA_PREP_UNLOCK" In
enum dma_ctrl_flags.

enum dma_ctrl_flags {
DMA_PREP_INTERRUPT = (1 << 0),
@@ -202,6 +205,8 @@ enum dma_ctrl_flags {
DMA_PREP_CMD = (1 << 7),
DMA_PREP_REPEAT = (1 << 8),
DMA_PREP_LOAD_EOT = (1 << 9),
+ DMA_PREP_LOCK = (1 << 10),
+ DMA_PREP_UNLOCK = (1 << 11),
};

So these flags we get passed while preparing CMD descriptor in Crypto
driver. Based on these
flags only i am setting LOCK/UNLOCK flags on actual hardware descriptor
in BAM driver.
if (flags & DMA_PREP_CMD) {
if (flags & DMA_PREP_LOCK)
desc->flags |= cpu_to_le16(DESC_FLAG_LOCK);
>
> What is the life span of the locked state? Do you always provide a
> series of descriptors that starts with a LOCK and ends with an UNLOCK?
> Or do you envision that the crypto driver provides a LOCK descriptor
> and
> at some later point provides a UNLOCK descriptor?
>

While preparing CMD descriptor we will use this LOCK/UNLOCK flags. So
if i wanted to write
some 20 registers of Crypto HW via BAM then i will prepare multiple
command descriptor
let's say 20 CMD descriptor so in the very first CMD descriptor I will
set the LOCK (DMA_PREP_LOCK ) flag and
in the the last CMD descriptor I will set the UNLOCK (DMA_PREP_UNLOCK
) flag.

>
> Finally, this patch just adds the BAM part of things, where is the
> patch
> that actually makes use of this feature?
>
Yes , this patch will add BAM part of things. For Crypto i will push
another patch
which will use this feature.

> Regards,
> Bjorn
>
>> >
>> > The point here is that this seems to be internal to dma and should be
>> > handled by dma driver.
>> >
>> This LOCK/UNLOK flags are part of actual hardware descriptor so this
>> should be handled by BAM driver only.
>> If we set condition like this
>> if (flags & DMA_PREP_CMD) {
>> do_lock_bam();
>> Then LOCK/UNLOCK will be applied for all the CMD descriptor
>> including
>> (QPIC driver, QUP driver , Crypto driver etc.).
>> So this is not our intension. So we need to set this LOCK/UNLOCK
>> only for
>> the drivers it needs. So Crypto driver needs
>> locking mechanism so we will set LOCK/UNLOCK flag on Crypto driver
>> request
>> only for other driver request like QPIC driver,
>> QUP driver will not set this.
>>
>> > Also if we do this, it needs to be done for specific platforms..
>> >
>>
>>
>>
>>
>>
>>
>>
>> > Thanks

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